ES6全面来袭

var a= 1;
if(true){
    var a = 2;
}
console.log(a); //2

var v='Hello World';
(function(){
alert(v);
var v='Hello Test';
})()

(function(){
  var a = 'a';
  var b = 'b';
  var c = 'c';
})()

(function(){
  var a,b,c;
  a = 'a';
  b = 'b';
  c = 'c';
})()

var v = 'Hello World';
(function(){
  var v;
  alert(v);
  v = 'Hello Test';
})();

var SIZE = 10;  // 用大写定义变量约定为常量，后面不去修改

if(true){
    let a = 2;
}
console.log(a); // Uncaught ReferenceError: a is not defined(…)

console.log(a); //undefined
console.log(b); //Uncaught ReferenceError: b is not defined(…)
var a = 'a';
let b = 'b';

 // 报错 Uncaught SyntaxError: Identifier 'a' has already been declared
function c() {
  let a = 10;
  var a = 1;
}
// 报错 Uncaught SyntaxError: Identifier 'a' has already been declared
function d() {
  let a = 10;
  let a = 1;
}

const SIZE = 10;
size = 20; //报错 Uncaught SyntaxError: Identifier 'SIZE' has already been declared

var a = 1;
var b = 2;
var c = 3;

var [a, b, c] = [1, 2, 3];

var { bar, foo } = { foo: "aaa", bar: "bbb" };
foo // "aaa"
bar // "bbb"

var fun = v => v;
// 等同于
var fun = function (v) {
    return v;
}

//如果箭头函数不需要参数或需要多个参数，就使用一个圆括号代表参数部分。
var f = () => 5;
// 等同于
var f = function () { return 5 };
var sum = (num1, num2) => num1 + num2;
// 等同于
var sum = function(num1, num2) {
  return num1 + num2;
};

function Person() {
  this.age = 0;
  setInterval(function growUp() {
    // 在非严格模式下，growUp() 函数的 this 指向 window 对象
    this.age++;
  }, 1000);
}
var person = new Person();

function Person() {
  var self = this;
  self.age = 0;
  setInterval(function growUp() {
    self.age++;
  }, 1000);
}

function Person(){
  this.age = 0;
  setInterval(() => {
    // |this| 指向 person 对象
    this.age++;
  }, 1000);
}
var person = new Person();

var link = function (height, color, url) {
    var height = height || 50;
    var color = color || 'red';
    var url = url || 'http://simmin.github.io';
}

var link = function(height = 50, color = 'red', url = 'http://simmin.github.io') {
}

$('#result').append(
  'There are <b>' + basket.count + '</b> ' +
  'items in your basket, ' +
  '<em>' + basket.onSale +
  '</em> are on sale!'
);

$('#result').append(`
  There are <b>${basket.count}</b> items
   in your basket, <em>${basket.onSale}</em>
  are on sale!
`);

$('#list').html(`
<ul>
  <li>first</li>
  <li>second</li>
</ul>
`);

var x = 1;
var y = 2;
`${x} + ${y} = ${x + y}`
// "1 + 2 = 3"
`${x} + ${y * 2} = ${x + y * 2}`
// "1 + 4 = 5"
function fn() {
  return "Hello World";
}
`foo ${fn()} bar`// foo Hello World bar

function Person (name, age) {
    this.name = name;
    this.age = age;
}
// 利用原型绑定方法，不会每次实例化都创建，提升性能
Person.prototype.say = function () {
    console.log('My name is ' + this.name + '. I`m ' + this.age + ' years old');
}
var han = new Person('韩梅梅', 16)

class Person {
    constructor(name, age) {
        this.name = name;
        this.age = age;
    }
    say() {
        console.log('My name is ' + this.name + '. I`m ' + this.age + ' years old');
    }
}

class Woman extends Person {
    constructor (name, age) {
        super(name, age) // 通过 super 调用父类的同名方法
    }
}

class Person {
    constructor (name, age) {
        this.name = name;
        this.age = age;
    }
    say () {
        console.log('My name is ' + this.name + '. I`m ' + this.age + ' years old');
    }
    static desc () {
        console.log('this is a static function');
    }
}
Person.desc() //this is a static function
var han = new Person('韩梅梅', 16)
hong.desc() // Uncaught TypeError: han.desc is not a function(…)

class Person {
  static Person() {
    console.log('this is a static function');
  }
}
class Woman extends Person {
}
Woman.Person(); // this is a static function

//正确写法
class Person {
}
Person.age = 20;
Person.age // 20
//错误写法
class Person {
  // 写法一
  age: 20
  // 写法二
  static age: 20
}
Person.age // 报语法错误